Behaviors

A behavior (also knows as mixin) can be used to enhance the functionality of an existing component without modifying the component's code. In particular, a behavior can "inject" its own methods and properties into the component, making them directly accessible via the component itself. A behavior can also respond to events triggered in the component, thus intercepting the normal code execution. Unlike PHP's traits, behaviors can be attached to classes at runtime.

Using behaviors

A behavior can be attached to any class that extends from Component. In order to attach a behavior to a class, the component class must implement the behaviors method. As an example, Yii provides the AutoTimestamp behavior for automatically updating timestamp fields when saving an Active Record model:

class User extends ActiveRecord
{
    // ...

    public function behaviors()
    {
        return [
            'timestamp' => [
                'class' => 'yii\behaviors\AutoTimestamp',
                'attributes' => [
                    ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
                    ActiveRecord::EVENT_BEFORE_UPDATE => 'updated_at',
                ],
            ],
        ];
    }
}

In the above, the class value is a string representing the fully qualified behavior class name. All of the other key-value pairs represent corresponding public properties of the AutoTimestamp class, thereby customizing how the behavior functions.

Creating your own behaviors

To create your own behavior, you must define a class that extends [[yii\base\Behavior]].

namespace app\components;

use yii\base\Behavior;

class MyBehavior extends Behavior
{
}

To make it customizable, like [[yii\behaviors\AutoTimestamp]], add public properties:

namespace app\components;

use yii\base\Behavior;

class MyBehavior extends Behavior
{
    public $attr;
}

Now, when the behavior is used, you can set the attribute to which you'd want the behavior to be applied:

namespace app\models;

use yii\db\ActiveRecord;

class User extends ActiveRecord
{
    // ...

    public function behaviors()
    {
        return [
            'mybehavior' => [
                'class' => 'app\components\MyBehavior',
                'attr' => 'member_type'
            ],
        ];
    }
}

Behaviors are normally written to take action when certain events occur. Below we're implementing events method to assign event handlers:

namespace app\components;

use yii\base\Behavior;
use yii\db\ActiveRecord;

class MyBehavior extends Behavior
{
    public $attr;

    public function events()
    {
        return [
            ActiveRecord::EVENT_BEFORE_INSERT => 'beforeInsert',
            ActiveRecord::EVENT_BEFORE_UPDATE => 'beforeUpdate',
        ];
    }

    public function beforeInsert() {
        $model = $this->owner;
        // Use $model->$attr
    }

    public function beforeUpdate() {
        $model = $this->owner;
        // Use $model->$attr
    }
}